Internal combustion engines may include water injection systems that inject water into a plurality of locations, such as into an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Engine water injection provides various benefits such as an increase in fuel economy and engine performance, as well as a decrease in engine emissions. In particular, when water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water, leading to charge cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, improved wide-open throttle performance, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx emissions, while a more efficient fuel mixture (reduced enrichment) may reduce carbon monoxide and hydrocarbon emissions.
Water injection systems include a water reservoir which may be refilled manually as well as opportunistically via water generated on-board the vehicle. For example, water in the form of condensate may be retrieved from one or more components, such as an EGR cooler, an AC evaporator, an exhaust heat exchanger, a charge air cooler, a vehicle external surface, etc. However, based on the source of the water, the quality of water injected into the engine may vary, affecting engine performance as well as potentially clogging the injection system.
Various approaches have been developed to test the flow of the water injection system. For example, the tests may determine whether the flow valve solenoids are energized, if the injection system is clogged, etc. One example approach is shown by Payling et al. in U.S. Pat. No. 6,553,753. Therein, a flow rate is varied and a flow error is learned based on a difference between the flow provided and the flow demanded. Based on the learned flow error, a shut-off valve of a water injection system is activated.
However, the inventors herein have identified potential issues with such an approach. As one example, the flow error may vary with engine conditions where water injection is applied. For example, during part throttle injection, small flow errors may not reflect clogging of the water injection system, however, the same magnitude of error during knock-limited engine operating conditions may reflect a higher degree of clogging. In addition, the smaller flow errors may have a larger impact on the engine performance at knock-limited engine operating conditions, or during catalyst cooling conditions. As another example, contaminants in the water may contribute to flow errors which may not be reliably differentiated from flow errors due to component issues. The nature of contaminants present in the water, as well as the degree of contamination, may vary widely based on where the vehicle operator refilled the water tank from. For example, it may be recommended to refill the water tank with distilled water, but the operator may refill with tap water or well water instead. This variation can result in minerals getting deposited on water filters, water injectors, engine parts, exhaust catalysts, etc. As yet another example, reliance on a single test to determine if the water injection system is functioning may be error prone due to the need to reliably detect relatively small changes in sensor data. Thus, a more robust functional test may be desired.
In one example, some of the above issues may be at least partly addressed by a method for an engine in a vehicle, comprising: predicting an expected injection error for a water injection system delivering water to the engine based on a quality of water in a water reservoir; if possible, estimating an actual injection error based on a change in engine parameters while ramping a water injection, and adjusting water injection to the engine based on either the actual error (if available), or based on the expected injection error. In this way, a water injection system on-board the vehicle may be reliably self-tested and the amount of water injected can be accurately controlled even with partial clogging.
As an example, a water tank of a vehicle may be refilled with water received from a remote location and/or with water collected during vehicle engine operation. The water may be injected during engine operation to leverage the charge cooling properties of water. Following refilling of the water tank, a quality (e.g., purity or usability) of the water may be assessed based on one or more properties of the water, such as conductivity, turbidity, particle matter content, etc. Based on the estimated water quality and the amount of time that the system is exposed to this water, a likelihood of clogging in a system delivering the water from the tank to the engine may be predicted. As such, clogging may result in a water injection error. Thus, an expected water injection error associated with the predicted likelihood of clogging may be determined and used as an initial estimate until the actual clogging level or injection error can be determined. When conditions allow a self-test, an actual injection error may then be determined based on a change in a set of engine operating parameters while a water injection is ramped in. The set of engine operating parameters may be selected based on the engine operating conditions at the time of the ramping in of a water injection. For example, the actual injection error may be learned based on a change in spark retard required to address knock when the ramping in is performed at high engine speed-high load conditions. Based on the actual error relative to the predicted error, a subsequent water injection (e.g., a timing, amount, and location of injection) to the engine may be adjusted. For example, water injection may be feed-forward adjusted based on the predicted error and then feedback adjusted based on the actual error. Further, a water injection window may be selected that better tolerates the level and nature of impurities in the water.
In this way, the flow of a water injection system may be reliably self-tested. The technical effect of learning a water injection error based on distinct sets of engine operating parameters at distinct engine operating conditions is that even small changes in sensory data can be reliably measured, thereby reducing errors in test results. In addition, a more robust self-test is enabled with reduced need for dedicated sensors. By correlating a water quality with errors in water injection, the water quality may be reliably assessed. In addition, system damage from contaminated water is reduced and parasitic losses and financial costs of purifying the water are minimized. The technical effect of integrating the water injection system with a control system that protects against contaminated water usage is that continued refilling of a water reservoir with contaminated water is reduced, extending engine component life. By improving water usage, the benefits of water injection can be extended.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.